1. Field of the Invention
This invention relates generally to a downhole measurement sensor assembly for an electrical submersible pump and method of manufacturing thereof, and more particular to a downhole measurement sensor assembly having a thin-film sensing element mounted to a rigid substrate and housed within a rugged, insulated and durable enclosure that is easily assembled and configured to be inserted into a windings area of a downhole motor of the electrical submersible pump.
2. Description of the Related Art
Various types of downhole equipment, such as pumps and similar devices, are used to move fluids from beneath the surface of the earth to the surface. Well known applications include oil and gas wells and water wells. A typical downhole arrangement would include a string composed of a series of tubes or tubing suspended from the surface. One type of well-known pump is a downhole electrical submersible pump (ESP). The ESP either includes or is connected to a downhole motor which is sealed so that the whole assembly is submerged in the fluid to be pumped. The downhole motor is connected to a three-phase power source at the surface and operates beneath the level of fluid downhole in order to pump the fluid to the surface.
A long power cable from the surface equipment (˜500 to 15,000 feet) generally provides power to the ESP and one or more downhole measurement sensors. The downhole measurement sensors are coupled to the ESP and used to monitor certain downhole parameters, such as pressure and temperature, of a subterranean bore-hole. The downhole measurement sensors generally include a sensing element that may utilize the substantially linear relationship of resistance and the particular downhole parameter in order to monitor the bore-hole conditions.
One type of downhole measurement sensor for monitoring downhole temperatures is a resistance temperature device (RTD) probe. RTD probes generally include a sensing element having a substantially linear relationship of resistance and temperature, thereby allowing the ESP motor temperature to be readily monitored by the circuitry in the RTD probe. RTD probes are physically deployed in the motor windings of the ESP motor, and monitor the temperature of the motor windings or motor oil in order to detect an impending motor failure due to abnormally high operating temperatures of the ESP motor.
In order to obtain relevant temperature readings from the winding area of the ESP motor, the RTD probe must be directly inserted into the motor oil within the small motor winding area. In addition, the RTD probe must be constructed to withstand high pressure, since the motor oil is typically at a pressure approximately equal to the well bore pressure, e.g., up to about 8000 psi. Moreover, because the RTD probe is positioned adjacent to the motor windings that carry high voltage and current, the probe must be electrically isolated in a non-metallic enclosure.
Many of the commercially available RTD probe assemblies consist of either a wire-wound element or a thin-film element placed inside a stainless steel sheath enclosure that is sealed on one end and with wires protruding from the other end. The inside of the enclosure is potted or sealed with a thermally conductive compound. For some probes, the combination of the stainless steel sheath enclosure and the space for the potting compound results in the RTD probe being physically too large to insert into the motor windings.
Another approach has been to utilize an RTD probe consisting of just the thin-film element placed inside a thin-wall thermoplastic polymer (polytetrafluoroethylene) sleeve, and having two insulated lead wires bonded to the leads of the thin-film RTD element. The construction of this RTD probe, however, involves connecting the insulated lead wires to the very small fragile lead wires of the thin-film sensing element. This causes difficulty in the manufacturing process, and also allows the RTD probe to be easily damaged during assembly or usage by breaking one of the connections of the lead wire to the thin-film sensing element.
It is therefore desirable to provide an improved downhole measurement sensor assembly for an electrical submersible pump and method of manufacturing thereof.
It is further desirable to provide a downhole measurement sensor assembly housed within a rugged, insulated and durable enclosure that is easily assembled and is configured to be inserted into a windings area of a downhole motor of the electrical submersible pump.
It is still further desirable to provide a method of manufacturing a downhole measurement sensor assembly by mounting a thin-film sensing element to a rigid substrate, connecting the leads of the thin-film sensing element to insulated lead wires of the downhole measurement sensor assembly, and housing the constructed sensor assembly in a rugged, insulated and durable enclosure.
It is therefore desirable to provide a downhole temperature sensor assembly having increased durability during assembly with independent connection points on a connection member between the leads of a thin-film temperature sensing element and insulated lead wires of the sensor.
Other advantages and features of the invention will be apparent from the following description and from the claims.